Refrigerant mixture for low back pressure condition

ABSTRACT

There is provided a composition of refrigerant mixtures for low back pressure condition, comprising isobutane, 1,1-difluoroethane and, optionally, additive selected from the group consisting of carbon oxide, trifluoromethyl iodide and mixture thereof. The composition according to the present invention is environment-friendly and can be directly drop in the conventional refrigerator system adopting CFC-12 refrigerant without any systemic change.

FIELD OF THE INVENTION

[0001] The present invention relates to a composition of refrigerantmixtures for low back pressure condition, which is environment-friendlyand can be directly dropped in the conventional refrigerator systemadopting CFC-12 refrigerant without any systemic change such that it canbe effectively used as a substitution material for Freon refrigerantCFC-12 which is the main cause of ozone layer destroy and green houseeffect of earth. More specifically, the present invention relates to thecomposition of refrigerant mixtures for low back pressure condition,containing isobutane, 1,1-difluoroethane, and, optionally an additive.The composition according to the present invention is environmentallyfriendly, therefore minimizes destroy of the ozone layer and globalgreen house effect. Further, it has many excellent properties such ashigh volumetric cooling capacity or the vapor pressure similar withCFC-12 to minimize the systemic modification of the refrigerator systemsadopting Freon refrigerant CFC-12, and azeotropic characteristic tominimize the temperature grade during evaporation and condensationprocesses.

DECRIPTION OF THE BACKGROUND ART OF THE INVENTION

[0002] Refrigerating cycle is composed of a compressor, a condenser, anevaporator, an expansion valve, a dryer, an oil separator, a liquidseparator, and so forth. Based on the 2^(nd) law of thermodynamics, therefrigerator absorbs heat from the low heat supply and emits it to thehigh heat supply with the assistance of the compressor's work.Refrigerant used in the refrigeration cycle absorbs the heat from thesurrounding and evaporates in the evaporator under the low temperature.In the compressor, the refrigerant is compressed to the gas having hightemperature and high pressure and then, it is cooling again in thecondenser and the phase thereof is changed to the liquid having highpressure. Finally, the pressure thereof is decreased to the initialvalue on passing through the expansion valve. During these cycles, theheat is transferred from the low heat supply, i.e., surrounding to thehigh heat supply and the refrigerant performs continuous cooling of thesurrounding.

[0003] According to operation temperature, the refrigerant is classifiedinto 3 classes: a refrigerant for low back pressure condition, arefrigerant for high back pressure condition, and a refrigerant formiddle back pressure condition. The refrigerant for low back pressurecondition operates at a temperature of −35˜−15° C. The refrigerant formiddle back pressure condition and the refrigerant for high backpressure condition are −15˜+5° C. and −10˜+10° C., respectively. As arepresentative example of the refrigerant for low back pressurecondition, CFC-12 (CF₂Cl₂, simply, R-12), one of CFC(Chlorofluorocarbon) refrigerant, can be mentioned. Due to its highcoefficient of performance and low flammability, CFC-12 has being widelyused in small refrigerators such as household and industrialair-conditioner. However, the use thereof is strictly restricted forbeing a main cause of ozone layer destroy and global green house effect.

[0004] For these reasons, the development of CFC-12 substitutionrefrigerants has been continuously progressed. HFC (Hydrofluorocarbon)refrigerants such as HFC-134a (or R-134) or HFC-152a (or R-152a),azeotropic refrigerants such as R-500, HC (Hydrocarbon) refrigerantssuch as R-600a, and an organic compound ammonia (NH₃) were suggested assubstitution refrigerants for CFC-12.

[0005] HFC refrigerants have been widely used as a substitutionrefrigerant for CFC-12, but there are questions as to the environmentalsafety of such HFC's. Especially, since HFC-134a (CH₂FCF₃), most widelyused among HFC refrigerants, has lower volumetric cooling capacity andcoefficient of performance with high compressing ratio than CFC, itconsumes more electricity than CFC-12 refrigerant does. Because of itspoor compatibility with a refrigerating oil, special oils like esteroils or poly alkylene glycol (PAG) oils are necessarily required ratherthan mineral oils. However, the ester oils or PAG oils may causesignificant damages to a refrigerator by the absorption of moisture whenthey are exposed to the air. For these reasons, they cannot be directlydropped in the refrigerator systems adopting CFC-12 refrigerant. Thatis, systemic changes of the conventional refrigerator systems such as acompressor and the manufacturing equipments are necessarily required.Also, the HFC refrigerants are not environment-friendly. Specifically,the global warming potential (GWP) of HFC-134a is about 300 (CO₂=1, 100yr), which is very high.

[0006] Although R-500 (CF₂Cl₂/CHF₂Cl₂) is an excellent refrigerantshowing azeotropic behavior, which is a mixture of 2 kinds ofrefrigerants but acts as a single refrigerant, the use thereof is alsorestricted because it contains Freon refrigerant which causesenvironmental pollution and destroys ozone layer.

[0007] The hydrocarbon refrigerants have been actively researched as asubstitution refrigerant for CFC-12, because of its excellentthermodynamic properties and low global warming potential, specifically3 (CO₂=1, 100 yr). For instance, isobutane, R600a refrigerant issuggested as a refrigerator for use in household. Despite of itsexcellent thermodynamic properties, it suffers from disadvantages thatit requires systemic changes or modifications of the CFC-12 refrigeratorsystems such as a compressor because of its low volumetric coolingcapacity. Further, it may also be susceptible to flammability andexplosiveness. In addition, R-290 (propane) having high volumetriccooling capacity, which is one of the refrigerant for high back pressurecondition, cannot be directly dropped in the conventional refrigeratorsbecause it has much higher vapor pressure than CFC-12. Non-azeotropicrefrigerant containing mixture of isobutane and propane is also sufferedfrom non-azeotropic behavior showing 5˜6° C. of temperature grade duringcondensing and evaporating processes as well as flammability andexplosiveness.

[0008] In addition, ammonia (NH₃) shows excellent refrigerant feature incooling capacity, but it is a poisonous gas and susceptible toflammability and explosiveness. Further, it erodes copper and its alloyby the absorption of moisture. Therefore, it cannot be used in therefrigerator for use in household.

[0009] Meanwhile, U.S. Pat. No. 5,624,595 disclosed a refrigerantcomposition comprising silicone oil as an additive in order to improveflammability of the refrigerant. However, the amount of silicone oiladded is strictly restricted because it circles through therefrigerating cycle as liquid state and reduces the cooling capacity andaccumulation thereof in the evaporator may cause significant damages tothe refrigerator. Further, since it is separated from the refrigerantwhile it is stored for a long time after being manufactured, theimprovement in flammability is relatively low when the real refrigerantis discharged as a gas from the vessel.

[0010] As a result, in order to use the refrigerants suggested in theabove, systemic changes or modifications of the refrigerator systemsadopting CFC-12 refrigerant is necessarily required for the reason thatthey have different properties than CFC-12 in terms of cooling capacity,condensing pressure, evaporating pressure, and so forth. This systemicchanges waste enormous cost and resources and the cost required formodifying manufacturing equipments is incalculably high.

[0011] Therefore, it has been demanded to develop new azeotropicrefrigerant, which could be directly dropped in the conventionalrefrigerator systems in which CFC-12 was used as a refrigerant such thatsystemic changes can be minimized, which has excellent volumetriccooling capacity, high performance coefficient, and evaporating pressurefeature without showing temperature grade during evaporating andcondensing processes, and which is compatible with components of therefrigerator system such as refrigerating oil.

SUMMARY OF THE INVENTION

[0012] Therefore, the object of the present invention is to provide acomposition of refrigerant mixture for low back pressure condition,which is environmentally friendly and is applied, with the adjustment ofthe amount of the refrigerant, directly to the conventional refrigeratorsystems adopting CFC-12 refrigerant without any systemic change.

[0013] Another object of the present invention is to provide acomposition of refrigerant mixture for low back pressure condition whichhas excellent coefficient of performance and safety to environment andhuman, condensing and evaporating pressures almost identical to that ofCFC-12, excellent compatibility with a refrigerating oil, and enhancednon-flammability and non-explosiveness.

[0014] The objects and other objects described in the description can beachieved by providing a composition of refrigerant mixture for low backpressure condition, containing isobutane and 1,1-difluoroethane, andoptionally an additive which increases non-flammability.

[0015] According to the first aspect of the present invention, there isprovided a composition of refrigerant mixture for low back pressurecondition containing isobutane and 1,1-difluoroethane.

[0016] According to the second aspect of the present invention, there isprovided a composition of refrigerant mixture for low back pressurecondition containing 25˜35 wt % of isobutane and 65˜75 wt % of1,1-difluoroethane.

[0017] According to the third aspect of the present invention, there isprovided a composition of refrigerant mixture for low back pressurecondition isobutane and 1,1-difluoroethane and an additive selected fromthe group consisting of carbon dioxide (CO₂), trifluoromethyl iodide(CF₃I) and mixture thereof to increase non-flammability.

[0018] According to the fourth aspect of the present invention, there isprovided a refrigerator system comprising as a refrigerant thecomposition of refrigerant mixture for low back pressure condition.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention relates to a composition of refrigerantmixture for low back pressure condition, which is environment-friendlyand can be directly dropped in refrigerator systems adopting CFC-12refrigerant, which is main cause of destruction of ozone layer and ofinduction of green house effect of earth,

[0020] The composition according to the present invention containsazeotropic mixture of isobutane and 1,1-difluoroethane, and optionallyan additive which improves non-flammability.

[0021] More specifically, the composition according to the presentinvention contains 25˜35 wt % of hydrocarbon refrigerant isobutane and65˜75 wt % of HFC refrigerant 1,1-difluoroethane (CHF₂CH₃), andoptionally less than 5 wt % of an additive, which is selected from thegroup consisting of carbon dioxide (CO₂), trifluoromethyl iodide (CF₃I)and mixture thereof in order to improve non-flammability, based on thetotal weight of refrigerant mixture,

[0022] According to the particular preferred embodiment of the presentinvention, a composition of refrigerant mixture for low back pressurecondition comprising 29˜31 wt % of isobutane, 68˜70 wt % of1,1-difluoroethane, 1˜2 wt % of an additive selected from the groupconsisting of carbon dioxide (CO₂), trifluoromethyl iodide (CF₃I), andmixture thereof gave most preferred result.

[0023] The additive, carbon dioxide (CO₂) or trifluoromethyl iodide(CF₃I), which is used to prevent flammability of the hydrocarbonrefrigerant, has additional role to improve volumetric cooling capacityand mobility of the refrigerant oil in the evaporator. According toanother preferred embodiment of the present invention, addition of 1.5wt % and 5 wt % of the additive to the refrigerant mixture raised theignition point of the refrigerant composition to about 745˜725° C. andto about 830˜850° C., respectively, and the ignition point was increasedin proportional to the content thereof However, since the excess contentof the carbon dioxide (CO₂) and/or trifluoromethyl iodide (CF₃I) couldlower the cooling capacity, it is desirable for the composition tocontain less than 5 wt % of the additive, based on the total weight ofrefrigerant mixture.

[0024] The composition according to the present invention can beprepared by removing air from an airtight vessel with a vacuum pump,followed by introducing the hydrocarbon refrigerant isobutane [CH(CH₃)₃]and HFC refrigerant 1,1-difluoroethane into the vessel and mixing therefrigerant mixture for a certain time. If necessary, carbon dioxide(CO₂) and trifluoromethyl iodide (CF₃I) can be added to the mixture inorder to prevent flammability of the hydrocarbon refrigerant and toincrease mobility of the refrigerating oil in the evaporator andvolumetric cooling capacity of the refrigerant composition. The obtainedproduct can be put into valve-equipped gas vessels and shipped. Theseprocesses can be performed at normal temperature.

[0025] According to the preferred embodiment of the present invention,the composition according to the present was proven to have highcoefficient of performance and volumetric cooling capacity. As thus, itcan be widely used in the refrigerator systems composed of a compressor,a condenser, and an expansion valve, and an evaporator. It can be alsoused in refrigerator systems equipped with an oil separator and a liquidseparator additionally. Especially, the composition exhibits similarbehaviors with CFC-12 in terms of vapor pressure, such that it can bedirectly dropped without any systemic change or modification in theconventional refrigerator systems in which CFC-12 is used as arefrigerant, comprising reciprocal, rotary or scrolling compressor.

[0026] In addition, since the composition according to the presentinvention is environment-friendly and no harm to the ozone layer andgreen house effect of earth, disadvantages resulted from CFC-12, HFC andHCFC refrigerant compositions can be avoided.

[0027] Further, since the composition has the excellent compatibilitywith the refrigerating oil which is used in order to prevent theabrasion of the parts such as a compressor, various refrigerating oilsdefined in the standard (ISOVG 10˜50) of the International StandardsOrganization (ISO) can be widely used. Especially, differently fromHFC-134a, mineral oils, which have been used most widely, can be used asa refrigerating oil.

[0028] The composition according to the present invention is alsoapplicable to the refrigerators adopting the heat pump method, where theheat emitted from the condenser of the refrigerating cycle is used asthe heating source. For example, the composition can be applied to theheat pump air-conditioner, which can be used for heating and cooling, byobtaining heat from the air in an evaporator located in the outdoor, andthen warming the air in the indoor with the heat emitted from acondenser.

[0029] The present invention will be described in more detail referringto the following Examples, but it should be understood that the scope ofthe present invention is not limited thereto.

EXAMPLE Example 1

[0030] Five compositions of refrigerant mixture for low back pressurecondition were prepared by the method described above. The formulationsare summarized in the Table 1: TABLE 1 ADDITIVE Recipe CH(CH₃)₃ CHF₂CH₃CO₂ CF₃I Recipe 1 29.5 69.0 1.5 0 (SR-10a) Recipe 2 29.5 69.0 0 1.5(SR-10b) Recipe 3 30.0 70.0 0 0 (SR-10c) Recipe 4 24.6 73.9 1.5 0(SR-10d) Recipe 5 34.5 64.0 0 1.5 (SR-10e)

Example 2

[0031] The thermodynamic properties of the recipes 1 to 5 (hereinafter,SR-10a to 10e) obtained from Example 1, such as boiling point, toxicitydata, ignition temperature, thermal conductivity, heat of evaporation,ozone layer destroy potential (ODP), and global warming potential (GWP)were measured and compared to CFC-12, HFC-134a, HFC-152a, and R-600 inTable 2: TABLE 2 Refrigerant Item R12 R134a R152a R600a R290 SR-10aSR-10b SR-10c SR-10d SR-10e Chemical CF₂Cl₂ CH₂FCF₃ CHF₂CH₃ C₄H₁₀ C₃H₈HC- HC- HC- HC- HC- formula Mixture Mixture Mixture Mixture MixtureMolecular 120.9 102.0 66.1 58.1 44.1 63.3 65.7 63.7 63.7 65.7 WeightBoiling −29.8 −26.5 −24.0 −11.7 −42.1 −20.3 −20.5 −20.3 −20.9 −19.7Point (° C.) Toxicity none none none none none none none none none noneIgnition none None 680 460 470 725 745 615 735 735 Temperature Themalconductivity (W/m. K) Liquid 0.08 0.0938 0.118 0.1064 0.1064 0.115 0.1150.115 0.115 0.114 Vapor 0.0089 0.0118 0.0124 0.0146 0.0163 0.013 0.0130.013 0.013 0.013 Heat of Vapor 149.8 198.7 307.1 355.7 374.5 303.0298.0 298.0 319.0 324.0 (kJ/kg)[at 0° C.] Refrigerating Mineral EsterMineral Mineral Mineral Mineral Mineral Mineral Mineral Mineral Oil ODP1 0 0 0 0 0 0 0 0 0 GWP 6900 1300 140 3 3 96 97 99 105 92 (CO₂ = 1, 100yr)

[0032] As shown in Table 2, the compositions according to the presentinvention, SR-10a to 10e could contain mineral oil as a refrigeratingoil and had zero value of ODP and 96˜97 of GWP which are very excellent,and higher ignition point compared to the hydrocarbon refrigerants(R-600a, R-290). In addition, they were non-toxic and had excellent heattransfer characteristic, and had low molecular weight such that theamount added can be reduced.

Example 3

[0033] The characteristics of SR-10a to 10e prepared in Example 1 werecalculated with NIST program and compared to those of CFC-12, HFC-134a,R-600a, and R600a/R290(40/60). The results thereof were summarized inTable 3 (The volumetric efficiency of the compressor is assumed to100%). TABLE 3 Theoretical performance of refrigerants in ASHRAE LBPconditions R600a/ R290 R12 R134a R152a R600a (40/60) SR-10a SR-10bSR-10c SR-10d SR-10e Cond. Mid Temp. 54.4 54.4 54.4 54.4 54.4 54.4 54.454.4 54.4 54.4 ° C. Cond. Mid Press. 1354 1470 1312 761.4 1392 1402 13951400 1419 1375 kpa Inlet(Vapor) T. ° C. 54.4 54.4 54.4 54.4 57.31 54.5154.47 54.42 54.46 54.9 Outlet(Liquid) T. 54.4 54.4 54.4 54.4 51.52 54.2954.33 54.38 54.33 53.9 ° C. Δt Condensation 0 0 0 0 5.79 0.22 0.14 0.040.13 1.0 ° C. Evap. Mid Temp. −23.2 −23.3 −23.3 −23.3 −23.3 −23.3 −23.3−23.3 −23.3 −23.3 ° C. Evap. Mid Press. 132.8 114.8 104.6 62.4 136.0132.0 130.0 131.0 131.5 129.2 kpa Inlet(L + V) T. ° C. −23.3 −23.3 −23.3−23.3 −26.2 −23.28 −23.25 −23.29 −23.15 −22.8 Outlet(Vapor) T. −23.3−23.3 −23.3 −23.3 −20.6 −23.34 −23.35 −23.31 −23.44 −23.8 ° C. ΔtEvaporation ° C. 0 0 0 0 5.63 0.06 0.01 0.02 0.29 1.0 Pressure Ratio10.07 12.80 12.54 12.19 10.23 10.62 10.73 10.68 10.79 10.64(P_(o)/P_(c)) Discharge Temp. 126.7 118.8 137.6 102.4 113.5 119.8 115.9119.6 121.8 118.1 ° C. p₁(Suc. Density) 6.496 4.714 2.778 1.451 2.6833.380 3.380 3.380 3.388 3.287 kg/m³ Volumetric Capa. 220.7 209.1 192.5116.5 222.2 227.1 226.6 226.8 228.9 222.7 kal/m³ Δh(Evap.)Capa. 33.0744.36 69.3 80.27 82.84 67.17 67.05 67.10 67.56 67.76 kal/kg COP w/w 2.712.73 2.69 2.89 2.71 2.78 2.77 2.78 2.77 2.77

[0034] Table 3 shows that the ratios of the volumetric cooling capacityof R600a and R134a to CFC-12 were 47% and 5.2%, respectively. But, therefrigerant mixture (SR-10 Series) according to the present inventionhad superior volumetric cooling capacity to CFC-12 by 3%. In terms ofcoefficient of performance (COP), R600a was most excellent and R134a hadsimilar value with CFC-12. The compositions according to the presentinvention (SR-10 Series) had higher COP than CFC-12 by about 2.5%.Further, the refrigerant mixtures (SR-10 Series) had a condensing andevaporating pressure similar to that of CFC-12. Compressing ratiothereof was about 6.2%, which is higher than CFC-12 and about 14.6%higher than R134a.

[0035] Because the compositions according to the present invention(SR-10a to SR-10e) had excellent cooling capacity and high COP, it wouldbe readily understood that they could be wildly used as a refrigerantfor low back pressure condition. Especially, the compositions could bedirectly dropped in the refrigerating systems in which CFC-12 are usedas a refrigerant, because they exhibited similar properties with CFC-12in terms of vapor pressure characteristics. Finally, the compositionsshowed azeotropic behavior such that the temperature grade during theevaporation and condensation could be reduced.

Example 4

[0036] With the equilibrium experimental apparatus composed of anequilibrium apparatus, a tank for recovering refrigerant, and atemperature controller for an equilibrium apparatus,temperature-dependent saturated pressure was measured for thecompositions according to the present invention (SR-10 Series). Theequilibrium experiment was carried out as follows: the temperature ofthe thermostat was set to a certain value, and the air inside therefrigerating cycle was removed with vacuum pump such that the pressurethereof was adjusted to 1×10⁻⁵ torr. Liquid compositions of refrigerantmixture were introduced to the equilibrium cell up to ⅓ of its volume.After that, the magnetic pump was operated to mix the compositions andto achieve equilibrium state. Once equilibrium state is achieved, thetime-dependent saturated pressure was measured with a temperature sensorand a pressure sensor.

[0037] As shown in Table 4, the compositions of refrigerant mixture forlow back pressure condition, SR-10a, SR-10b, and SR-10c showed similarvapor pressure characteristics in a low temperature region with CFC-12.Even though there were small gap in the high temperature region, such agap was proven to be ignorable, compared to R134a. TABLE 4 RefrigerantPressure (kPa) Temp. (° C.) R12 R134a SR-10a SR-10b SR-10c 60 1516.41682.1 1591.0 1578.5 1581.5 55 1356.5 1490.8 1421.0 1404.5 1407.5 501208.4 1317.3 1265.0 1240.0 1243.0 45 1074.1 1159.4 1122.0 1106.5 1109.540 950.5 1016.2 991.5 974.5 977.5 0 303.3 292.5 311.4 308.5 308.5 −20148.4 132.6 150.7 145.6 147.6 −25 120.9 106.2 123.2 120.8 121.8 −30 99.384.6 99.8 95.1 97.1 −35 80.7 67.0 80.0 78.9 79.2 −40 64.0 51.3 63.5 61.962.3

Example 5

[0038] With the second refrigerant calorimeter described on the KoreanIndustrial Standard (KS B 6365-1987), various capacities for SR-10a,SR-10b, and SR-10c prepared in Example 1 were measured and compared toCFC-12 and HFC-134a that are low back pressure refrigerants. The resultsthereof were summarized in Table 5. TABLE 5 The Capacities of therefrigerants from calorimeter under ASHRAE LBP condition Item Cur-Evap/Cond. Capacity Input COP rent Temp. Glide Refrig. (kal/hr) (W)(W/W) (A) (° C.) Remark R12 196.5 159.1 1.435 0.75 0/0 *Com- R134a 184.2153.7 1.392 0.74 0/0 pressor: SR-10a 205.8 159.7 1.497 0.78 0.0/0.1 PL25SR-10b 203.8 158.7 1.493 0.75 0.0/0.1 *Ref.-oil: SR-10c 204.5 158.01.503 0.76  0.0/0.03 Freol S-22T

[0039] As shown in Table 5, the compositions according to the presentinvention, SR-10a, SR-10b, and SR-10c has excellent cooling capacity andhigh COP, compared to R12 and R134a. As thus, they could be used in therefrigerator systems as a refrigerant low back pressure condition.

Example 6

[0040] To a refrigerant mixture consisting of 30 wt % of isobutane and70 wt % of 1,1-difluoroethane, various amounts of carbon dioxide (CO₂)or trifluoromethyl iodide (CF₃I) was added, and then, ignitiontemperature for each composition was measured. The Results thereof weresummarized in Table 6. In this experiment, the air was added to thecomposition in a ratio of 60 vol % because, under such condition, thecomposition comprising 30 wt % of isobutane and 70 wt % of1,1-difluoroethane based on the total weight of refrigerant mixture wasproven to be most ignitable. TABLE 6 Additives CF₃I Mixture ratio 0%1.5% 5% 10% 20% 30% 40% 50% (weight %) Ignition Temp. 615 745 850 9551050 1200 1300 None (° C.) CO₂ Mixture ratio 0% 1.5% 5% 10% 20% 30% 40%50% (weight %) Ignition Temp. 615 725 830 925 1020 1170 1260 None (° C.)

[0041] As shown in Table 6, the ignition temperature was remarkablyincreased by the addition of carbon dioxide (CO₂) or trifluoromethyliodide (CF₃I). However, as the amount added exceeds 5 wt %, coolingcapacity and COP might be reduced. Therefore, it is desirable to addthese additives less than 5 wt %.

Example 7

[0042] To test the reliability of the refrigerator system in which thecompositions according to the present invention, SR-10a, SR-10b, andSR-10c, used as a refrigerant, reliability evaluating experiment with acompressor was performed according to the standard of GE company in US.The results thereof were shown in Table 7: TABLE 7 RefrigerantCompressor Freezer oil R12 R-134a PL25 PL25 SR-10a SR-10b SR-10c MineralEster PL25 Item (Freol S-22T) (Freol a-22T) Mineral (Freol S-22T) WearNo No No No No Ref. Oil Color L0.5 L0.5 L0.5 L0.5 L0.5 (ASTM) TAN 0.0080.010 0.005 0.006 0.004 (0.1↓) (mgKOH/ g) Water 0 0 0 0 0 (20 ppm↓)

[0043] As shown in Table 7, the compositions, SR-10a, SR-10b, andSR-10c, exhibited very high compatibility with various refrigeratingoils, especially with a mineral oil (Freol S-22T, trade mark). Further,abrasive characteristic of the compositions in both valve and frictionparts of the machine was proven to be almost identical with that ofCFC-12.

INDUSTRIAL APPLICABILITY

[0044] The compositions of refrigerant mixture for low back pressurecondition according to the present invention can substitute CFC-12refrigerant in which the use thereof are highly restricted for being aharmful material to environment according to the Montreal protocol.Further, they can be directly dropped in the refrigerating systems inwhich CFC-12 was used as a refrigerant without any systemic change ormodification such that the cost required for the manufacture ofrefrigerating systems could be highly reduced. The advantages of thecompositions according to the present invention is as follows: a) Lowevaporating temperature under atmospheric pressure; b) Equal or similarlevel of condensing/evaporating pressure compared to CFC-12; c)Excellent latent evaporating heat; d) Low condensing point; e) Excellentvolumetric cooling capacity; f) High critical temperature; g) Excellentcompatibility with the refrigerating oil; h) Low viscosity and high heattransferring characteristic; i) Excellent electric insulation propertywithout the deposit of electric insulating material; j) Remarkablyincreased non-flammability and non-explosiveness; k) safety toenvironment and human; and l) Direct applicability to the refrigeratingsystems adopting CFC-12 refrigerant without any systemic change.

1. (Amended) A refrigerant composition for use in low back pressurecondition containing a refrigerant and an additive, wherein a) therefrigerant is a mixture of isobutane and 1,1-difluoroethane, thecontent of the isobutane is in an amount of 25˜35 wt %, the content ofthe 1,1-difluoroethane is in an amount of 65˜75 wt % and the sum of theisobutane and the 1,1-difluoroethane is 100 wt % based on the totalweight of the refrigerant, b) the additive is selected from the groupconsisting of carbon dioxide (CO₂), trifluoromethyl iodide (CF₃I) andmixture thereof which prevents flammability of the isobutane, thecontent of the additive is in an amount of less than 5 wt % based on therefrigerant, and c) the refrigerant composition shows an azeotropicbehavior.
 2. (Deleted)
 3. (Deleted)
 4. (Amended) The refrigerantcomposition as set forth in claim 1, wherein, based on the total weightof the refrigerant composition, the content of the isobutane is 29˜31 wt%, the content of the 1,1-difluoroethane is 68˜70 wt % and the contentof the additive is 1˜2 wt %.
 5. (Amended) A refrigerator system,comprising the refrigerant composition of claim 1.